Hot tub water care basics

A hot tub holds a few hundred gallons of very warm water, often with several people in it. Georgia's health department notes that warm water helps germs like Legionella grow and that high heat makes disinfectant less effective. The good news: the routine is short, and it doesn't take much chemical.

The numbers to keep

The CDC's hot tub guidance is simple. Free chlorine at least 3 ppm, or bromine at 4 to 8 ppm. pH between 7.0 and 7.8. That's higher chlorine than a pool needs, and on purpose: CDC's pool code notes that the germ behind hot tub rash came back quickly in spas when chlorine fell below 3 ppm.

The CDC also recommends not using stabilizer (cyanuric acid) in hot tubs, because it slows disinfection. That matters if you use dichlor, which adds stabilizer every time you dose it. Regular water changes keep it from building up.

The full chart for hot tubs is on the ideal levels page.

Dosing: small amounts, measured carefully

Hot tub doses are tiny, so measure. A kitchen scale that reads grams helps. Here's what raising free chlorine by 3 ppm takes in a 400-gallon tub:

Product	Amount for 400 gallons
56% dichlor	0.29 oz
6% unscented bleach	2.6 fl oz
65% cal-hypo	0.25 oz

Use the hot tub calculator for your tub's size and your products, including pH and alkalinity. Add one chemical at a time and let it mix in before adding the next.

How often to test

The CDC says to test chlorine and pH at least twice a day, and more when the tub gets heavy use. Hot tub makers suggest less: Caldera says at least once a week. At the very least, test before anyone gets in. Write it down on the test log; it has hot tub targets printed at the top.

Draining and refilling

Hot tub water wears out, and the CDC and every hot tub maker we checked say to replace it on a schedule.

The CDC's Legionella toolkit gives a formula for how often to replace the water:

Days between water changes = (gallons ÷ 3) ÷ average number of daily users

AQUA Magazine and Jacuzzi use the same formula. Jacuzzi's example: a 200-gallon tub with 4 people a day should be drained about every 16 days. A 400-gallon tub used by 2 people a day works out to about 67 days.

Sundance and Caldera both say every 3 to 4 months is typical. Use whichever comes first. Drain sooner if the water foams, turns cloudy, smells or won't stay balanced; Jacuzzi and Sundance both list those signs.

When you drain, turn the power off at the breaker first so the pump can't run dry (Sundance's advice), and scrub every surface before you refill. The CDC's toolkit says to scrub surfaces each time the tub is drained.

Cleaning the filter

Hot tub filters catch a lot. Brands give different schedules, so check your manual, but here's the general range. Sundance says to clean the filter every 2 to 4 weeks, soak it in filter cleaner every 3 to 4 months and replace it every 1 to 2 years. Jacuzzi says rinse weekly, deep clean every 4 to 6 weeks and replace every 12 to 24 months. Rinse more often when the tub gets heavy use.

Before and after you soak

Shower before you get in. The CDC recommends it, and HealthLinkBC says it cuts down the germs and body oils that use up chlorine. Afterward, the CDC says to take off your swimsuit, shower with soap and wash the suit. Those three steps help prevent hot tub rash.

Know what you're preventing

Hot tub rash is an itchy, red, bumpy rash, often worse where the swimsuit held water. The CDC says it's caused by Pseudomonas bacteria and mild cases usually clear up within a few days. The Virginia Department of Health describes it the same way.

Legionella is more serious. People catch it by breathing mist or steam from a contaminated hot tub, and it can cause Legionnaires' disease, a dangerous type of pneumonia. The Georgia Department of Public Health says people over 50, smokers and anyone with a weakened immune system are at higher risk. The CDC's prevention list is the routine on this page: right chlorine and pH, frequent testing, scrubbing away slime, filter care and regular water changes.

Temperature and safety

Keep the water at 104°F or below. The CPSC, the CDC and CDC's pool code all set that as the maximum.

1. Pregnancy: the CDC says to talk to a healthcare provider before using a hot tub. The CPSC advises keeping water at or below 100°F.
2. Kids: the CDC says children under 5 shouldn't use hot tubs. The CPSC suggests special caution for young children.
3. Alcohol: skip it. The CPSC warns that drinking raises the risk of drowning in a hot tub.
4. Time: keep soaks short. HealthLinkBC says no more than 10 minutes at a time, and Alabama's health department warns that going past 15 minutes can cause overheating.

That's the whole routine. Test, dose small, change the water on schedule and keep the filter clean, and your hot tub stays clear and safe.